1. Field of the Invention
The present invention relates to a semiconductor light emitting device composed of BN (boron nitride), GaN (gallium nitride), AlN (aluminum nitride), InN (indium nitride) or TlN (thallium nitride) or an III-V group nitride based semiconductor (hereinafter referred to as a nitride based semiconductor) which is their mixed crystal.
2. Description of the Background Art
In recent years, nitride based semiconductor laser devices which emit light in blue or violet have been studied and developed as light sources for recording or reproduction used for high-density and large-capacity optical disk systems. In the high-density and large-capacity optical disk systems, an improvement in recording and reproducing speed is required with an increase in capacity. For achievement of it, it is necessary for nitride based semiconductor laser devices as light sources to operate at high frequency.
FIG. 17 is a cross-sectional view showing the structure of a conventional semiconductor laser device described in JP-A-10-321962.
The semiconductor laser device shown in FIG. 17 is obtained by forming, on an n-SiC substrate 21, an n-buffer layer 22 composed of GaN, an n-cladding layer 23 composed of Al0.1Ga0.9N, an active layer 24 composed of undoped In0.32Ga0.68N, and a p-cladding layer 25 composed of Mg doped Al0.1Ga0.9N in this order.
A ridge portion is formed in the p-cladding layer 25. An n-surface evaporation protective layer 26 composed of Al0.5Ga0.95N is formed on a flat portion of the p-cladding layer 25 and on sidewalls of the ridge portion. An Mg highly doped Al0.5Ga0.95N layer 20 is further formed on an upper surface of the ridge portion. An n-current blocking layer 27 composed of Al0.15Ga0.85N is formed on the n-surface evaporation protective layer 26. A p-contact layer 28 composed of Mg doped GaN is formed on the n-current blocking layer 27 and the Mg highly doped Al0.05Ga0.95N layer 20. A p-side electrode 29 is formed on the p-contact layer 28, and an n-side electrode 30 is formed on the reverse surface of the n-SiC substrate 21.
As shown in FIG. 17, in the conventional semiconductor laser device having the n-current blocking layer 27 on both sides of the ridge portion and the flat portion of the p-cladding layer 25, when the pulse width is shortened under pulsed operation, response characteristics of the rise time and the fall time of light output power are degraded.